The present invention relates to a superconducting coil device with a coil winding comprising at least two superconducting strip conductors and contacts for connecting the coil device to an external circuit.
Coil devices are known in the field of superconducting machines and superconducting magnetic coils in which superconducting wires or strip conductors are wound into coil windings. Conductors in the form of wires are usually used for classical low-temperature superconductors such as NbTi and Nb3Sn. High-temperature superconductors or also high-Tc superconductors (HTS) on the other hand are superconducting materials with a critical temperature of above 25 K and for a few classes of material of above 77 K. These HTS conductors are typically available in the form of flat strip conductors, having a strip-type substrate strip and a superconducting layer disposed on the substrate strip. In addition the strip conductors often have even further layers such as stabilization layers, contact layers, buffer layers and in some cases also insulation layers. The most important class of material of the so-called second-generation HIS conductors (2G-HTS) are compounds of the type REBa2Cu3Ox, wherein RE stands for an element of the rare earths or a mixture of such elements.
The substrate strip typically consists of either steel or the alloy Hastelloy. Electrical contact to an external circuit is mostly established via a contact layer made of copper, wherein this contact layer is either applied on one side above the super conducting layer or can surround the entire strip conductor as an enveloping layer. In both versions it is better to establish the contact on the upper side, i.e. on the side of the substrate strip which bears the superconducting strip. With contacting on the rear side, i.e. on the side of the substrate facing away from the superconducting layer, higher contact resistances occur, which leads to greater electrical losses and an increased need for cooling in these areas.
With a superconducting coil winding, in which a number of layers of a strip conductor lie in a number of turns above one another, it is often difficult to contact both ends of the coil winding on the upper side. With standard winding techniques used for manufacturing disk windings the upper side of the strip conductor will usually be facing inwards either on the inner side or on the outer side of the winding. In order, despite this, to create a low-resistance contact on the upper side of the strip conductor, with known coil devices a specially designed contact piece is used, which is pushed into the winding on the upper side of the strip conductor. However a complex manufacturing process is needed for such a coil device since, to guarantee the mechanical stability needed, particular measures must be taken at the location of this contact piece. If a wet winding process with an epoxy adhesive is used then first of all a filler piece, made of Teflon for example, must be inserted in order to keep the points to be contacted free from adhesive. After removal of the filler piece, for contacting this point for example, a solder connection to a contact piece made, of copper can be established. However since this contact lies within the winding, to establish the necessary mechanical stability of the contact area, it must be fixed retroactively with bandages made of glass fiber reinforced plastic and epoxy adhesive.